1. Field of the Present Invention
This invention relates to a new high efficiency, abrasion-resistant fluorocarbon polymer composite which has substantially improved properties over a wide range of temperature and load conditions. More particularly, the invention is directed to abrasion-resistant, anti-friction tubing and particularly liners for use as wire insulation and in push-pull cable assemblies. It is fabricated from a mixture of polymers of tetrafluoroethylene (hereinafter called PTFE), a polymer of arylene sulfide, and optionally a filler.
Use of the liners of the present invention is contemplated in automobile, aviations, marine, electrical, and industrial engineering applications. In addition to reciprocating motion, this tubing can be used for rotary motion, such as speedometer assemblies, linear unidirectional motion, such as conveying mechanisms for feeding cable, solder and flexible welding wire, or for motion typical in the use of wire insulation. Additionally, the fluorocarbon composite may be utilized in applications where resistance to cold flow is essential.
2. Prior Art Statement
Fluorocarbon polymers are materials which are well known in the art. Polytetrafluoroethylene resins have heretofore been utilized in extruded tubular products, however, in its pure form it has proved to wear too rapidly and therefore has required use of fillers to enhance its wear resistant properties. See U.S. Pat. No. 3,409,584. Likewise, it is broadly known to incorporate a fluorocarbon polymer with an arylene sulfide polymer, however, efforts to produce an arylene-sulfide-polymer-filled PTFE extruded tubular product have heretofore been found to result in a poor quality product.
In U.S. Pat. No. 4,075,158, issued to Coale, a flexible extruded product was fabricated from a mixture of a polyphenylene sulfide and a filler selected from a group of fillers with at least one of the fillers being PTFE. The patent requires the polyphenylene sulfide to be present in an amount of at least approximately 30% by weight and that the polytetrafluoroethylene be present in the mixture in an amount of at least 20% by weight of the total mixture. Other fillers which can be added to the mixture of polyphenylene sulfide and PTFE include: glass fibers, asbestos fibers, molybdenum disulfide, carbon fillers, and the like.
Recently in Lubrication Engineering, Volume 33, pages 33 to 38, it was reported that polypheylene sulfide ("PPS")/PTFE sintered parts exhibit compressive modulus higher than any filled PTFE compound and that this high compressive modulus accounts for a thirty-fold reduction in wear rate of the polyphenylene sulfide/PTFE surface and mating surface when compared with glass filled PTFE. This report compares sintered parts having 20 and 40 weight percent polyphenylene sulfide present and indicates better compressive strengths and reductions in wear rate at 40 weight percent. These findings are consistant with the Coale Patent which requires that polyphenylene sulfide be present in an amount of at least 30% by weight.
In U.S. Pat. No. 4,026,863, issued to Iseki, et al., a fluorocarbon polymer composite is disclosed, which comprises a fluorocarbon polymer and a filler in the form of powder, granules, beads, fiber, or the like. The filler is further disclosed as being given a surface treatment utilizing polyphenylene sulfide. Iseki discloses applying polyphenylene sulfide to the surface of the filler (comprising 80 weight parts maximum based upon 100 weight parts PTFE). As disclosed, the maximum amount of polyphenylene sulfide permitted in a composition containing 100 parts PTFE and filler is about 10 weight percent, and preferably from 2 to 5 weight percent, based upon the filler. Also, implicit in Iseki, et al., is that when more usual amounts of filler are utilized, say 20 to 30 parts per 100 parts PTFE, the amount of polyphenylene sulfide present in the composition is less than 1% by weight. Moroever, it is further disclosed that when the amount of polyphenylene sulfide is greater than the above limits, the characteristics of the fluorocarbon polymer composite containing the filler are deteriorated by imparting properties of the polyphenylene sulfide.
We have found that many compositions suggested in the art are unacceptable when applied to products made by extrusion, and particularly, when the ultimate product is an extruded tubular product. Furthermore, it has been found that when the extruded product must be abrasion-resistant anti-friction type tubing for use in a range of temperatures and load conditions, many prior art compositions and properties of such compositions deteriorate, thus excluding them from effective use in such an environment.
One of the typical uses of extruded tubular products of the present invention is in automotive applications where, for example, the products are exposed to temperatures ranging from minus 40.degree. F. to plus 400.degree. F. and where they are required to convey a movement through crowded compartments which often mandates serpentine routing. Thus the motion is conveyed in an environment where the distribution of forces and contact area is constantly changing.
We have likewise found that previous teachings, developments, and data do not account for the above diverse conditions. Moroever, data related to rotary bearings or compressor piston rings is not helpful in predicting performance in the above abrasion-resistant, anti-friction tubing applications, and in fact, the traditional ASTM test (eg. tensile strength, elongation, hardness, specific gravity) cannot be utilized to predict or guarantee performance of tubing in the aforementioned environment.
It is therefore an object of the present invention to provide a fluorocarbon polymer composite which is compatible with fabricating extruded liners.
It is another object to provide high efficiency, abrasion-resistant, anti-friction, extruded tubing for use as liners in unidirectional, reciprocating, or rotary cable assemblies.
It is yet another object to provide abrasion-resistant dialectric insulating material which has excellent resistance to cold flow.
It is a further object to provide abrasion-resistant, anti-friction tubing which operates efficiently in a wide range of temperatures and load conditions in complex and serpentine type routing environments.
It is still a further object to provide fluorocarbon polymer composite liners which operate efficiently and effectively in complex routing environments at temperatures ranging from -40.degree. F. to 400.degree. F.
It is still yet a further object to provide a fluorocarbon polymer composite which has a tendency to arrest and/or offset the effects of stress relaxation, which generally occur over a period of time.
Other objects and advantages of the present invention will become apparent from the following description taken in connection with the accompanying drawings and examples wherein it is set forth by way of illustration certain embodiments of the present invention.